Brass alloy

ABSTRACT

The invention relates to a brass alloy substantially consisting of copper and zinc. The alloy has at least one additional alloy component. A lead content is at most 0.1 weight percent. The zinc fraction is 40.5 to 46 weight percent. The alloy comprises a mixed crystal having fractions of an alpha micro structure and of a beta microstructure. The weight proportion of the beta microstructure is at least 30% and at most 70%.

The invention relates to a brass alloy for use in the manufacture of semi-finished products intended for chip-removing processing, wherein the brass alloy consists essentially of copper and zinc, and wherein the brass alloy has at least one additional alloy component.

This type of brass alloy is frequently used as semi-finished product in the form; of strip or wire, and is subsequently further processed into end products. The further processing frequently takes place with the use of cutting processes.

When brass is being cut, it has been found advantageous in the past to add lead to the alloy to the extent of up to four percent by weight. The lead has a positive effect as a chip breaker, extends the tool service life, and reduces one cutting forces. The important material parameters, such as strength and corrosion resistance, are not negatively influenced by the addition of lead.

In spite of the positive properties of lead, there are attempts, among others supported by the directives of EU-Directive 2000/53/EG concerning scrap vehicles and Directive 2002/96/EG concerning electric and electronic scrap devices, to replace lead as a cutting element in brass.

However, the tests carried out so far with alternative alloy variations have not resulted in materials which meet the requirements made of them. These alloys are either significantly more expensive than lead-containing alloys, lead to an excessively high tool wear, or also contain alloys which are environmentally problematic.

In the manufacture of brass alloys it is attempted to achieve a good cutting property, as well as a good deformability. It has been found difficult to simultaneously meet both requirements in an optimum manner, because as a rule all measures which positively reinforce a desired property-lead to a reduction of the second property. Typically, a compromise is selected such that a high strength with simultaneously sufficient, deforming capability is predetermined.

Therefore, it is the object of the present invention to define a lead-free brass alloy of the above-mentioned type which has a good cutting capability, sufficient mechanical-properties, and generates as little wear as possible of the cutting tools used.

Moreover, it is the object of this invention to minimize the content of ecologically harmful alloy elements.

Furthermore, this invention is based on the object to achieve certain properties through the targeted combination of elements which are not environmentally problematic, as well as through the manufacturing process.

In particular, this applies to the properties:

-   -   Good cutting capability,     -   high strength, but still sufficiently good ductility,     -   good hot and cold deformability,     -   sufficient corrosion resistance.

In addition, an economically sensible mass production should be possible in the form of a semi-finished product.

The idea is based on the attempts mentioned, below for achieving the desired material properties:

-   -   a) The material structure is influenced by changing the         copper/zinc ratio in such a way that an alpha/beta crystal         mixture is present, in which the proportion of the beta/phase is         about 30 to 70%. Since the beta-phase exhibits a brittle         behavior under normal cutting conditions, its increased content         leads to a more favorable cutting behavior;     -   b) Additional alloy elements serve for stabilising the         alpha-phase and beta-phase, particularly during the finishing         process of the semi-finished product;     -   c) Furthermore, the cutting behavior, as well as the mechanical         properties, are influenced positively by the targeted addition         of elements which form further precipitations. On the one hand,         the precipitations facilitate a chip which breaks into short         pieces; on the other hand, grain fining is effected, so that an         improved ductility with high strength is achieved;

d) A fourth advantage can be achieved by influencing the arrangement or orientation of the two phases, alpha and beta and/or the precipitations, in order to thereby adjust in a targeted manner the processing properties (for example, by a combination of deforming or heat treatment).

For adhering to the requirements according to the invention, it has been found especially advantageous that a content of lead is at most 0.1% by weight, and the proportion of zinc is 405 to 46% by weight, and the proportion of copper is at most 59% by weight, and that the alloy contains a mixed crystal with proportions of an alpha-structure as well as of a beta-structure, wherein the proportion by weight of the beta-structure is at least 30% and at most 70% and the proportion of any additional alloy components is at most 1.0% by weight, and the sum of the proportions of all additional alloy components is at least 0.5% by weight.

It may happen that, depending on the type of application, certain properties of the alloy are particularly desirable. For this purpose, it is provided to add individual alloy elements mentioned above in a respectively higher concentration, without increasing the total amount of alloy elements (except for copper and zinc).

The precipitations contained in the structure, which can be found also in the soft alpha-structure, influence the cutting behavior positively.

The alpha-structure of the mixed crystal forms a cubic/surface centered spatial structure. On the other hand, the beta mixed crystal forms a cubic space-centered structure.

It has been found particularly advantageous if the proportion of the beta-structure is at least 50%. This is particularly reinforced by the fact that a zinc content of about 42% by weight is present.

The elements iron and nickel have a regulative influence on the growth of grain of the alpha-phase and beta-phase, wherein nickel additionally facilitates the stabilization of the beta-structure. Proportions which are too high lead to brittleness of the alloy.

The elements tin, silicon, manganese and iron stabilize and increase the proportion of the beta-phase.

For improving the corrosion resistance, the addition of phosphorus may be provided. In particular, a maximum content of phosphorus in the range of 0.1% by weight is being considered,

In accordance with a typical alloy composition, it is provided that the proportion of copper is 54 to 59.0% by weight.

Furthermore, it is provided that the proportion of zinc is 40 to 46% by weight,

A first additional alloy component is defined by the fact, that the proportion of iron is 0.1 to 0.5% by weight. Iron serves for controlling the grain size of the alpha-phase and the beta-phase, proportions smaller than 0.1% have no sufficient effect. Proportions of greater than 0.5% would lead to substantial iron precipitation which acts negatively on the mechanical properties of the alloy.

In particular, it is considered that the proportion of iron is 0.2 to 0.3% by weight.

A second additional alloy component is defined in that the content, of nickel is 0.1 to 0.5% by weight. Nickel stabilizes the alpha-phase.

In particular, it is considered that the proportion of nickel is 0.2 to 0.3% by weight.

A third additional alloy component is defined in that the proportion of silicon is 0.01 to 0.20% by weight. Silicon stabilizes the beta-phase and, together with other elements, forms fine precipitations which have a positive effect on the cutting behavior and are responsible for grain fining.

In particular, it is being considered that the proportion of silicon is 0.03 to 0.08% by weight.

A fourth additional alloy component is defined in that the proportion of manganese is 0.01 to 0.20% by weight. Manganese stabilizes the beta-phase and, together with other elements, forms fine precipitations which act positively on the cutting behavior and are responsible for grain fining

In particular, it is considered that the proportion of manganese is 0.03 to 0.08% by weight.

A fifth additional alloy component is defined in that the proportion of tin is 0.1 to 0.5% by weight.

In particular, it is considered that the proportion of tin is 0.2 to 0.3% by weight.

Phosphorus leads to an improved corrosion-resistance of the alloy, in particular phosphorus acts also for the removal of zinc.

Contributing to an optimum composition of the alloy, is the fact that the proportion of elements which are not copper, zinc, iron, nickel, silicon, manganese, or tin, is less than 0.2% by weight.

A preferred embodiment of the alloy has, with respect to its composition, preferably the following proportions by weight. Copper in the range of 54% to 59.5%, zinc in the range of 36% to 40.5%, iron in the range of 0.1% to 0.5%, nickel in the range of 0.1% to 0.5%, silicon in the range of 0,01% to 0.2%, manganese in the range of 0.01% to 0.2%, tin in the range of 0.1% to 0.5% and lead in a proportion of at most 0.1%. The lead content of the alloy is also caused by the use of scrap in the manufacture of such alloys, at the most 0.1%.

In correspondence with the proportions of the above additions, the proportions of copper and/or zinc are reduced as necessary.

In accordance with a particularly preferred embodiment, the proportion of copper is 57.0% to 57.5%, the proportion of zinc is 41.9% to 42.5%, the proportion of nickel is 0.2% to 0.3%, the proportion of iron is 0.2% to 0.3%, the proportion of silicon is 0.03% to 0.08%, the proportion of manganese is 0.03% to 0.08%, the proportion of tin is 0.2% to 0.3% and the proportion of lead is less than 0.1%. Moreover, it is particularly being considered that the sum of the proportions by weight of all additional possible components is at most 0.2%.

With respect to the compositions mentioned above, it. is basically possible to add to the alloy only some of the recited elements. However, in accordance with an especially preferred embodiment, it is considered to add all of the aforementioned elements with a proportion by weight within the respectively defined intervals in combination with each other.

In accordance with a typical embodiment, it is provided that the lead content is within an interval of 0.01% to 0.1%. As a result or the relation according to the invention, between the alpha mixed crystal and the beta mixed crystal the desired material properties can be achieved, even with reduced lead contents. In this connection, the alpha mixed crystal leads to a relatively good deformability of the alloy and imparts viscous properties to the alloy. The beta mixed crystal, on the other hand, is relatively poorly deformable and is brittle. All these properties are desirable for a good cutting capability. Consequently, due to the relation of the alpha-components and the beta-components, the alloy is imparted with a sufficient toughness for supporting deformability and a sufficient brittleness for supporting a cutting capability.

Aside from the pure relation between the alpha-components and the beta-components, it has also been found to be advantageous to influence the grain size of the mixed crystals. It has been found to be positive, to support relatively small and uniform grain sizes. By the addition of iron and silicon, iron silicides are formed which impair the growth of the grain and thereby have a positive influence on the structure as a result. The addition of tin and/or iron facilitates the formation of beta mixed crystals.

It is also found that, the addition of manganese, in combination with oxygen or phosphorus, facilitates the precipitation of oxides or phosphides and thereby leads to a finer grain structure. This, in turn, reinforces a good cutting capability. Also, in small quantities, proportions of phosphorus have been found to be advantageous with respect to the formation of structure.

With respect to the manufacture of the alloy, a preferred production process can be carried out In such a way that, initially extrusion is carried out in a temperature range of 600° to 750° C. This produces a structure which has a portion of the beta mixed crystal of about 50% by weight.

For reinforcing a good cutting capability, as well as a good deformability, it is possible to carry out. an intermediate annealing at a temperature of about 500° to 600° C. The intermediate annealing leads to a recrystallization and thus, to a formation of new grain. This reinforces the formation of a finely granular structure.

By carrying out a suitable intermediate annealing, it is possible to realize a proportion of the beta mixed crystal of 30 to 45 percent. As a result, an increased deformability of the semi-finished product is achieved.

In accordance with the invention, it is intended that the brass alloy of copper and zinc is produced with a lead content of 0.01 to 0.1 percent with at least one additional alloy component. This additional alloy component influences the structure of the mixed crystal in order to achieve the material properties which are desired for a specific application.

In accordance with another preferred embodiment, it is provided to realize the following alloy with respect to the percentages by weight.

Cu 55-56%, Fe 0.2-0.3%, Ni 0.1-0.2%, Si 0.01-0.03%, Mn 0.1-0.2%, Sn 0.3-0.5%, Zn remainder. This embodiment leads to an especially high proportion of beta mixed crystals between 55 and 70% beta-content, which causes an especially short breaking-chip.

Another preferred embodiment is made available with respect to percent by weight by the following alloy:

Cu 57-57.5%, Fe 0.2-0.3%, Ni 0.2-0.3%, Si 0%, Mn 0%, Sn 0,2-0.3%, Zn remainder. It is the object in this case to achieve a slightly increased alpha-proportion and precipitations which are less hard.

Moreover, it is also being considered with respect to preferred embodiments to realize the following alloy with respect to percent by weight.

Cu 56-56.5%, Fe 0.4-0.5%, Ni 0.2-0.3%, Si 0%, Mn 0.1-0.2%, Sn 0.35-0,5%, Zn remainder. This produces precipitations which are less hard and in its place, a formation of the precipitation of primarily precipitated iron is supported. The increased addition of manganese and tin produces an increased beta-proportion as compared to the preceding embodiment.

The brass alloy according to the invention, serves for manufacturing so-called semi-finished products which are subjected to at least one more processing step. Typical embodiments of such serai-finished products are wires, sections and/or rods. The next processing step Celsius at least one chip-removing process. Also, the next processing step may be a combination of a shaping and a chip-removing process. The shaping step can be carried out at room temperature or also at an increased temperature. With respect to the increased, temperatures, a half warm temperature of up to about 45° Celsius and a hot shaping temperature in a range of 600° Celsius up to 850° Celsius can be distinguished. 

1-19. (canceled)
 20. A brass alloy for use in manufacturing semi-finished products which is intended for a chip-removing processing, the brass alloy consisting essentially of copper and zinc, as well as at least one additional alloy component, wherein a content of lead is at most 0.1 percent by weight, the proportion of zinc is 40.5 to 46 percent by weight, and the proportion of copper is at most 59 percent by weight, and the alloy includes a mixed crystal with proportions of an alpha-structure as well as a beta-structure, wherein the proportion of the beta-structure is at least 30 percent by weight and at most 70 percent by weight, and the proportion of each additional alloy component is at most 1.0 percent by weight and a sum of proportions of all additional alloy components is at least 0.5 percent by weight.
 21. The brass alloy according to claim 20, wherein the proportion of copper is 54 to 59.0 percent by weight.
 22. The brass alloy according to claim 20, wherein the proportion of zinc is about 42 percent by weight,
 23. The brass alloy according to claim 20, including proportion of iron of 0.1 to 0.5 percent by weight.
 24. The brass alloy according to claim 23, wherein the proportion of iron is 0.2 to 0.3 percent by weight.
 25. The brass alloy according to claim 20, including a proportion of nickel of 0.1 to 0.5 percent by weight.
 26. The brass alloy according to claim 25, wherein the proportion of nickel is 0.2 to 0.3 percent by weight.
 27. The brass alloy according to claim 20, including a proportion of silicon of 0.01 to 0.20 percent by weight,
 28. The brass alloy according to claim 27, wherein the proportion of silicon is 0.03 to 0.08 percent by weight.
 29. The brass alloy according to claim 20, including a proportion of manganese of 0.01 to 0.20 percent by weight.
 30. The brass alloy according to claim 29, wherein the proportion of manganese is 0.03 to 0.08 percent by weight.
 31. The brass alloy according to claim 20, including a proportion of tin of 0.1 to 0.5 percent by weight.
 32. The brass alloy according to claim 31, wherein the proportion of tin is 0.2 to 0.3 percent by weight.
 33. The brass alloy according to claim 20, wherein a proportion of substances which are not copper, zinc, iron, nickel, silicon, manganese or tin, is less than 0.2 percent by weight.
 34. The brass alloy according to claim 20, wherein the proportion of the beta-structure is at least 50 percent by weight.
 35. The brass alloy according to claim 20, including by weight Cu 55-56%, Fe 0.2-0.3%, Ni 0,1-0.2%, Si 0.01-0.03%, Mn 0.1-0.2%, Sn 0.3-0.5%, remainder Zn.
 36. The brass alloy according to claim 20, including by weight Cu 57-57.5%, Fe 0.2-0.3%, Ni 0.2-0.3%, Si 0%, Mn 0%, Sn 0.2-0.3%, remainder Zn.
 37. The brass alloy according to claim 20, including by weight Cu 56-56.5%, Fe 0.4-0.5%, Ni 0.2-0.3%, Si 0%, Mn 0.1-0.2%, Sn 0.35-0.5%, remainder Zn.
 38. The brass alloy according to claim 20, including a maximum content of phosphorus of about 0.1% by weight. 